The present invention is related to a metering apparatus for liquids with means for holding a pipette point or syringe and with means for detaching the pipette point or syringe and an electric drive motor for moving a displacement member of a displacement device for aspirating or ejecting air into or from out a pipette point, or for moving coupling means adapted to be coupled with a syringe piston of the syringe. The means for detaching the pipette point or syringe are actuated separately in this, without that the displacement member or the syringe piston and the coupling means coupled therewith are moved. The invention relates further to a method for metering liquids using such a metering apparatus.
Metering apparatuses are mainly used in the laboratory for metering liquids. The liquid amounts to be metered are particularly located in the range of 100 nl up to several 100 ml. Metering apparatuses by which liquids are taken up in one single step and given off in one single step are designated as pipettes. Metering apparatuses by which liquids are taken up in one single or several steps and given off in plural steps are designated as dispensers.
The liquids are taken up in pipette points or syringes and given off from that. Pipette points are small pipes with an opening at the lower end and an opening at the upper end. The lower opening is mostly smaller than the upper opening is. Syringes have a syringe cylinder and a syringe piston, disposed movably in the syringe cylinder by shifting in the direction of the cylinder axis. Further, the syringe cylinder has a syringe opening in the syringe bottom, that is often disposed in a small pipe which projects from the syringe bottom.
When metering, the pipette point is held on the metering apparatus such that the upper opening is in communicating connection with a displacement device of the metering apparatus. The displacement device is mostly a cylinder with a piston that is shiftable therein. By moving the piston, an air cushion is moved, so that liquid is aspirated through the lower opening into the pipette point or is ejected from the same.
The syringe is held on the metering apparatus such that the syringe cylinder is stationary with respect to the metering apparatus, and the syringe piston is mechanically coupled to coupling means of the metering apparatus. By dislocating the coupling means, the syringe piston can be shifted in the syringe cylinder in order to aspirate liquid into the syringe cylinder and to eject it out of the same.
In order to move the displacement member or the coupling means, known metering apparatuses feature a manually driven drive mechanism or an electric drive motor. A metering apparatus with an electric drive motor is controlled by means of electric control means and it has an electric power supply connected to the electric drive motor and the electric control means (for instance an accumulator, a battery or a mains supply device). In addition, the electric control means are electrically connected to input means. Via the input means, metering steps (for instance to take up and to give off liquid) can be controlled, and/or the amounts of liquid to be taken up and to be given off can be selected and/or modes of operation (for instance pipetting or dispensing) can be selected. The input means can be electric touch-buttons or switches in particular. Further, metering apparatuses with an electric drive motor have often a display device (a LCD display for instance) in order to output information regarding the operating condition of the metering apparatus and/or the progress of a metering procedure and/or selected metering amounts and/or a selected mode of operation.
The means for holding the pipette point are mostly realised as a clamping seat (for instance as pin-up lug or blind hole). A passage opening in the front side of the pin-up lug or in the bottom of the blind hole, respectively, is communicatingly connected to the displacement chamber of the displacement device.
The means for holding the syringe are for instance cylinder gripping levers, which are associated to a cylinder accommodation in a casing of the metering apparatus in order to hold a flange on the syringe cylinder in the cylinder accommodation. Further, the means for holding can comprise piston gripping levers in a coupling dome, into which an end of the syringe piston or of a syringe piston rod is insertable in order to couple the same with the coupling dome.
Pipette points and syringes are detachably connected to the metering apparatus, so that they can be replaced by new pipette points or syringes after use. Thereby contaminations at subsequent meterings can be avoided. Pipette points or syringes for single use are available at low cost from plastic material.
The means for detaching a pipette point often comprise a throw-off slider having one end that is associated to the pin-up lug or the blind hole. The other end of the throw-off slider features an actuation button. A pipette point can be pushed off from the pin-up lug or be pushed out of the blind hole by displacing the throw-off slider.
In this, the means for detaching the pipette point or syringe is preferably arranged laterally on the outside of the base body and is not in connection with the displacement member of the displacement device, mostly the cylinder, or the movable coupling means of the metering apparatus in case that syringes are used.
In order to detach the syringe, the gripping levers may be pivotal towards the outside. For this purpose, the cylinder gripping levers can be provided with actuation ends that are manually actuable from the outside and have contact sites on the inner side which co-operate with actuation ends of the piston gripping levers, so that the piston gripping levers are moved upon actuation of the cylinder gripping levers when the syringe cylinder is completely thrust into the syringe piston. The means for detaching a syringe can also feature a mechanism which can be actuated by way of one single actuation button and acts on the cylinder gripping levers and the piston gripping levers. In particular, the means for detaching the syringe may bring about a detachment of the syringe from the metering apparatus, irrespective of the position of the syringe piston in the syringe cylinder.
In the metering apparatus with electric drive motor, detachment of a pipette point does not have any effects on the positioning of the piston in the cylinder of the displacement device. If the throw-off of the pipette point takes place for instance when the piston is in an upper position after the suction stroke, the piston must be dislocated into a base position by additional actuation steps, starting from which a completely new metering process can be initiated again. If a metering apparatus having an electric drive motor is laid aside after detaching the pipette point, the piston being in its upper position, and is thereafter used by another person, difficulties may arise when this person does not recognise that the piston must first be brought into a lower position for the metering in order to take up liquid by the metering apparatus.
Generally, for the user of a metering apparatus with controllable drive, an electric one in particular, it is not obvious in which position the actuation member or the coupling means is when he/she has thrown off the pipette point or syringe from the metering apparatus.
In a metering apparatus, there is also the situation in which the user wants to throw off a pipette point or syringe even though a liquid taken up or particles taken up together with the liquid, like magnetic beads, are at least partly still present in the pipette point or syringe. In this case, the displacement member or the coupling means, respectively, is not moved down up to the bottom, and the pipette point or syringe, respectively, is thrown off in spite of this by the means for detaching the pipette point or syringe, respectively, that is separate from the displacement device or the coupling means. As the position of the displacement member or of the coupling means, respectively, is not known for the next user of the metering apparatus in this situation, in particular when this user is another one than that one which has used the metering apparatus before, he/she does not known after putting up a new pipette point or syringe whether he/she has to move the displacement member or the coupling means downward at first in order to take up liquid by the metering apparatus, or whether the displacement member or the coupling means are already in the bottom position.
Similar problems may arise when a syringe is detached in a metering apparatus with electric drive motor before the syringe piston and with it the coupling means had been brought into its lower position.
The document U.S. Pat. No. 6,968,749 B2, the entire contents of this is incorporated herein by reference, discloses a portable automatic pipette with a throw-off device for pipette points. A sensor detects whether a pipette point has been removed. When the sensor detects the removal of a pipette point, a micro-processor controls the output of an alarm signal, in order to give notice to the user that an erroneous operation had occurred. The user has to set the pipette into the starting condition anew for a new metering process.
The solutions mentioned in the following from the following documents can also be applied to the metering apparatus and the process of the present invention. The description relevant to this is incorporated by reference into the following application.
From U.S. Pat. No. 5,187,990, the entire contents of this is incorporated herein by reference, a metering apparatus for pipette points having an electric drive and a throw-off device for pipette points is known. From this document, electric control means for controlling the dislocation of the piston of the displacement device and a method for metering liquids are also known, in which the piston is dislocated in a special manner.
U.S. Pat. No. 6,778,917 B1, the entire contents of this is incorporated herein by reference, US 2007/0276546 A1, the entire contents of this is incorporated herein by reference, and US 2008/0011042 A1, the entire contents of this is incorporated herein by reference, disclose apparatuses with electric control means, input means and display means. Special control—as well as input—and display methods are also known from these documents.
U.S. Pat. No. 7,434,448 B2, the entire contents of this is incorporated herein by reference, describes a metering apparatus with a throw-off device for pipette points. From this document, it is also known that the casing of the pipette features a casing upper part with a mechanical drive mechanism and a casing lower part detachably connectable therewith and having a displacement device. A disc on a piston rod of the piston is pressed against the end of a driving rod of the drive mechanism under spring pre-stress.
From US 2008/006100 A1, the entire contents of this is incorporated herein by reference, a metering apparatus with a casing upper part and a casing lower part and a coupling between the piston and the drive mechanism is known, the coupling comprising an elastic element.
U.S. Pat. No. 5,620,660, the entire contents of this is incorporated herein by reference, describes a metering apparatus with cylinder gripping levers and piston gripping levers for detachably holding syringes.